There are many applications where we need a train of radio frequency (rf) pulses, such as charged particle accelerators, radar and communication. Also, we need extremely narrow pulses with extremely high peak power for initial fusion. Usually the energy is built up in between pulses and is stored in the static electric field of capacitors, which discharge partially, as in a hard tube modulator, or completely, as in a line-type pulser, into an rf amplifier, which converts the stored electrostatic energy into rf energy. The conversion from direct current (dc) to rf takes place at high level and therefore is inefficient. The peak power is limited by the characteristics of the amplifier. The peak power of an electrostatic pulser can be increased by pulse compression using frequency modulation and a dispersive structure or using storage cavities with a phase shift keyer as described in U.S. Pat. No. 4,009,444. However, this requires both an electrostatic modulator and a pulse compression system, and the disadvantage of converting direct current energy into radio frequency at high level still remains. This invention, the radio frequency storage pulser (RASP), compresses into a narrow pulse the energy contained not in a wider pulse but the energy contained in a period.